Expand code generation to include conversions between date types

core/src/commonMain/generated/io/islandtime/_Conversions.kt

@@ -0,0 +1,55 @@
+//
+// This file is auto-generated by 'tools:code-generator'
+//
+@file:JvmMultifileClass
+@file:JvmName("DateTimesKt")
+
+package io.islandtime
+
+import kotlin.jvm.JvmMultifileClass
+import kotlin.jvm.JvmName
+
+/**
+ * Returns this year-month with the precision reduced to the year.
+ */
+fun YearMonth.toYear(): Year = Year(year)
+
+/**
+ * Returns this date with the precision reduced to the year.
+ */
+fun Date.toYear(): Year = Year(year)
+
+/**
+ * Returns this date with the precision reduced to the month.
+ */
+fun Date.toYearMonth(): YearMonth = YearMonth(year, month)
+
+/**
+ * Returns this date-time with the precision reduced to the year.
+ */
+fun DateTime.toYear(): Year = date.toYear()
+
+/**
+ * Returns this date-time with the precision reduced to the month.
+ */
+fun DateTime.toYearMonth(): YearMonth = date.toYearMonth()
+
+/**
+ * Returns this date-time with the precision reduced to the year.
+ */
+fun OffsetDateTime.toYear(): Year = dateTime.toYear()
+
+/**
+ * Returns this date-time with the precision reduced to the month.
+ */
+fun OffsetDateTime.toYearMonth(): YearMonth = dateTime.toYearMonth()
+
+/**
+ * Returns this date-time with the precision reduced to the year.
+ */
+fun ZonedDateTime.toYear(): Year = dateTime.toYear()
+
+/**
+ * Returns this date-time with the precision reduced to the month.
+ */
+fun ZonedDateTime.toYearMonth(): YearMonth = dateTime.toYearMonth()

core/src/commonMain/kotlin/io/islandtime/Conversions.kt

@@ -7,51 +7,6 @@ import io.islandtime.base.TimePoint
 import kotlin.jvm.JvmMultifileClass
 import kotlin.jvm.JvmName
 
-/**
- * Returns this date with the precision reduced to the year.
- */
-fun YearMonth.toYear(): Year = Year(year)
-
-/**
- * Returns this date with the precision reduced to the year.
- */
-fun Date.toYear(): Year = Year(year)
-
-/**
- * Returns this date-time with the precision reduced to the year.
- */
-fun DateTime.toYear(): Year = date.toYear()
-
-/**
- * Returns this date-time with the precision reduced to the year.
- */
-fun OffsetDateTime.toYear(): Year = date.toYear()
-
-/**
- * Returns this date-time with the precision reduced to the year.
- */
-fun ZonedDateTime.toYear(): Year = date.toYear()
-
-/**
- * Returns this date with the precision reduced to the year-month.
- */
-fun Date.toYearMonth(): YearMonth = YearMonth(year, month)
-
-/**
- * Returns this date-time with the precision reduced to the year-month.
- */
-fun DateTime.toYearMonth(): YearMonth = date.toYearMonth()
-
-/**
- * Returns this date-time with the precision reduced to the year-month.
- */
-fun OffsetDateTime.toYearMonth(): YearMonth = dateTime.toYearMonth()
-
-/**
- * Returns this date-time with the precision reduced to the year-month.
- */
-fun ZonedDateTime.toYearMonth(): YearMonth = dateTime.toYearMonth()
-
 /**
  * Returns the combined time and UTC offset.
  */

tools/code-generator/src/main/kotlin/io/islandtime/codegen/Main.kt

@@ -2,6 +2,7 @@ package io.islandtime.codegen
 
 import com.squareup.kotlinpoet.ClassName
 import io.islandtime.codegen.generators.ConstantsGenerator
+import io.islandtime.codegen.generators.DateConversionsGenerator
 import io.islandtime.codegen.generators.DatePropertiesGenerator
 import io.islandtime.codegen.generators.TemporalUnitGenerator
 import java.io.File
@@ -21,7 +22,8 @@ fun calendar(name: String) = ClassName(CALENDAR_PACKAGE_NAME, name)
 private val generators = arrayOf(
     TemporalUnitGenerator,
     ConstantsGenerator,
-    DatePropertiesGenerator
+    DatePropertiesGenerator,
+    DateConversionsGenerator
 )
 
 fun main() {

tools/code-generator/src/main/kotlin/io/islandtime/codegen/descriptions/DateTimeDescription.kt

@@ -4,35 +4,63 @@ import com.squareup.kotlinpoet.TypeName
 import io.islandtime.codegen.base
 
 enum class DateTimeDescription {
+    Year {
+        override val typeName: TypeName get() = base("Year")
+        override val smallestUnit: TemporalUnitDescription get() = TemporalUnitDescription.YEARS
+        override val simpleName: String get() = "year"
+        override val isDateBased: Boolean = true
+    },
+    YearMonth {
+        override val typeName: TypeName get() = base("YearMonth")
+        override val smallestUnit: TemporalUnitDescription get() = TemporalUnitDescription.MONTHS
+        override val simpleName: String get() = "year-month"
+        override val isDateBased: Boolean = true
+    },
     Date {
         override val typeName: TypeName get() = base("Date")
-        override val datePropertyName: String get() = "this"
+        override val smallestUnit: TemporalUnitDescription get() = TemporalUnitDescription.DAYS
         override val simpleName: String get() = "date"
+        override val isDateBased: Boolean = true
     },
     DateTime {
         override val typeName: TypeName get() = base("DateTime")
+        override val smallestUnit: TemporalUnitDescription get() = TemporalUnitDescription.NANOSECONDS
         override val datePropertyName: String get() = "date"
         override val simpleName: String get() = "date-time"
+        override val isDateBased: Boolean = true
     },
     OffsetDateTime {
         override val typeName: TypeName get() = base("OffsetDateTime")
+        override val smallestUnit: TemporalUnitDescription get() = TemporalUnitDescription.NANOSECONDS
         override val datePropertyName: String get() = "dateTime"
         override val simpleName: String get() = "date-time"
+        override val isDateBased: Boolean = true
     },
     ZonedDateTime {
         override val typeName: TypeName get() = base("ZonedDateTime")
+        override val smallestUnit: TemporalUnitDescription get() = TemporalUnitDescription.NANOSECONDS
         override val datePropertyName: String get() = "dateTime"
         override val simpleName: String get() = "date-time"
+        override val isDateBased: Boolean = true
     },
     Instant {
         override val typeName: TypeName get() = base("Instant")
-        override val datePropertyName: String get() = ""
+        override val smallestUnit: TemporalUnitDescription get() = TemporalUnitDescription.NANOSECONDS
         override val simpleName: String get() = "instant"
     };
 
     abstract val typeName: TypeName
-    abstract val datePropertyName: String
+    abstract val smallestUnit: TemporalUnitDescription
     abstract val simpleName: String
 
-    val isDateBased: Boolean get() = datePropertyName.isNotEmpty()
+    open val isDateBased: Boolean = false
+
+    open val datePropertyName: String get() = throw NotImplementedError()
+
+    open fun convertsDirectlyTo(other: DateTimeDescription): Boolean {
+        return isDateBased &&
+            other.isDateBased &&
+            other.smallestUnit > smallestUnit &&
+            other.smallestUnit > TemporalUnitDescription.DAYS
+    }
 }

tools/code-generator/src/main/kotlin/io/islandtime/codegen/descriptions/TemporalUnitDescription.kt

@@ -45,7 +45,8 @@ enum class TemporalUnitDescription(
     val intName: String get() = "Int$pluralName"
     val longName: String get() = "Long$pluralName"
     open val singularName: String get() = pluralName.dropLast(1)
-    val lowerCaseName: String get() = pluralName.toLowerCase(Locale.US)
+    val lowerSingularName: String get() = singularName.toLowerCase(Locale.US)
+    val lowerPluralName: String get() = pluralName.toLowerCase(Locale.US)
     val valueName: String get() = "value"
     val inUnitPropertyName: String get() = "in$pluralName"
     val inUnitUncheckedPropertyName: String get() = "${inUnitPropertyName}Unchecked"
@@ -86,7 +87,7 @@ data class TemporalUnitConversion(
 
     val constantName: String
         get() {
-            val (smallerUnit, largerUnit) = smallerUnitToLargerUnit()
+            val (smallerUnit, largerUnit) = orderedFromSmallerToLargerUnit()
             return "${smallerUnit.pluralName}_PER_${largerUnit.singularName}".toUpperCase(Locale.US)
         }
 
@@ -98,7 +99,7 @@ data class TemporalUnitConversion(
         }
 
     val constantValue: Long by lazy {
-        val (smallerUnit, largerUnit) = smallerUnitToLargerUnit()
+        val (smallerUnit, largerUnit) = orderedFromSmallerToLargerUnit()
 
         (smallerUnit.ordinal until largerUnit.ordinal)
             .map { TemporalUnitDescription.values()[it].conversionFactor.toLong() }
@@ -117,7 +118,7 @@ data class TemporalUnitConversion(
         }
     }
 
-    private fun smallerUnitToLargerUnit() = if (fromUnit <= toUnit) {
+    private fun orderedFromSmallerToLargerUnit() = if (fromUnit <= toUnit) {
         fromUnit to toUnit
     } else {
         toUnit to fromUnit

tools/code-generator/src/main/kotlin/io/islandtime/codegen/generators/DateConversionsGenerator.kt

@@ -0,0 +1,59 @@
+package io.islandtime.codegen.generators
+
+import com.squareup.kotlinpoet.FileSpec
+import io.islandtime.codegen.SingleFileGenerator
+import io.islandtime.codegen.descriptions.DateTimeDescription
+import io.islandtime.codegen.descriptions.DateTimeDescription.*
+import io.islandtime.codegen.descriptions.TemporalUnitDescription
+import io.islandtime.codegen.dsl.FileBuilder
+import io.islandtime.codegen.dsl.FunctionBuilder
+import io.islandtime.codegen.dsl.file
+
+object DateConversionsGenerator : SingleFileGenerator() {
+    override fun generateSingle(): FileSpec = buildDateConversionsFile()
+}
+
+private fun buildDateConversionsFile() = file(
+    packageName = "io.islandtime",
+    fileName = "_Conversions",
+    jvmName = "DateTimesKt"
+) {
+    DateTimeDescription.values().forEach { receiverClass ->
+        DateTimeDescription.values()
+            .filter { otherClass -> receiverClass.convertsDirectlyTo(otherClass) }
+            .forEach { otherClass -> buildConversionFunction(from = receiverClass, to = otherClass) }
+    }
+}
+
+private fun FileBuilder.buildConversionFunction(from: DateTimeDescription, to: DateTimeDescription) {
+    function(name = "to${to.name}") {
+        kdoc {
+            "Returns this ${from.simpleName} with the precision reduced to the ${to.smallestUnit.lowerSingularName}."
+        }
+
+        receiver(from.typeName)
+        returns(to.typeName)
+
+        if (from.smallestUnit < TemporalUnitDescription.DAYS) {
+            delegatesTo(from.datePropertyName)
+        } else {
+            construct(from, to)
+        }
+    }
+}
+
+private fun FunctionBuilder.construct(from: DateTimeDescription, to: DateTimeDescription) {
+    code {
+        when (to) {
+            Year -> {
+                require(from in arrayOf(Date, YearMonth)) { "Cannot construct '$to' from '$from'" }
+                "return Year(year)"
+            }
+            YearMonth -> {
+                require(from == Date) { "Cannot construct '$to' from '$from'" }
+                "return YearMonth(year, month)"
+            }
+            else -> throw IllegalArgumentException("Cannot construct '$to'")
+        }
+    }
+}